Helical ribbon spring measuring apparatus



A. HOYT Oct. 4, 1938.

. HELICAL RIBBON SPRING MEASURING APPARATUS Filed Dec'. 30, 1956 l atented Oct.4, 7 v I v v UNITED STATES PATENT-OFFICE.

'HELICAL RIBBON. srnmc MEASURING APPARATUS Archer Hoyt, Aspinwall, Pa., assignor to Gulf Rcsearch & Development. Company, Pittsburgh. Pa., a corporation of Delaware 3 Application December so, 1936, Serial No. 118,411

5 Claims. (01. 2651.4)

This invention relates to improvements in According to the present. invention I provide helical ribbon spring measuring apparatus; and a construction adapted to further reduce the it comprises, in apparatus for measuring stresses, level sensitivity of instruments having' helical a helical coil springformed of a wound-up thin ribbon springs, without introducing complica- '5 ribbon, means for applying stress along the axis tions, and with a considerable gain in rugged- '5 of the spring, whereby a rotational deflection of ness. According to the invention the upper porthe spring proportional to such stress is'protion of the spring is tapered down to a small duced, a portion of the helix adjacent one end diameter. That is, the uppermost few turns are thereof being-tapered down to .form a portion gradually diminished. in radius. The tapered of reduced diameter, and means for supporting end of the spring is rigidly attached to the sup- 10 the spring attached to the end of the ribbon at port. By this expedient, the level sensitivity of said tapered portion, whereby accurate measurethe apparatus is reduced by a'factor of 10 to 20, ment is secured even though the support be inso that the precision of leveling required for a correctly leveled or misaligned: allfas more fully tolerance of 0.1 milligal is 10 to seconds of S hereinafter set forth and as, claimed. arc. This improvement greatly facilitates field In a prior application, Serial No. 34,824, file operations and moreover-provides an instrument August 5, 1935 I have disclosed a gravimeter of which is especially rugged, by reason of the rigid the spring balance type, comprising a mass susattachment of spring to support. pended by 'a ribbon type coil spring. A coil In the accompanying drawing I have shown 20 spring formed of a wound-up thin ribbon of. more or less diagrammatically, two examples of 20 steel or other elastic material has the property a specific embodiment of the invention. Inthe of giving, on being subjected to axial stress, anv showings, 7 angular deflection. .The angular deflection is Fig. 1 isa view in elevation of a spring accord- I very nearly linearly proportional to the applied ing to the invention with associated parts making axial stress and may be taken as a measure oi. up a gravimeter; v g the stress. In the principal embodiment of the Fig. 2 shows what takesplace in the apparatus gravimeter disclosed in said application, the of Fig. 1 when the support is oil level;

mass is suspended by means of the ribbon spring, Fig. 3 is a detailed 'view showing cne manner the upper end of the spring being secured to a of attaching the spring to the support; and,

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V fixed support. A gravimeter is required to meas- .Fig. 4 illustrates the adaptation of the inven 30 I ure exceedinglyjsmall difierences in gravity; dittion to 8- bflrfl e ferences oi the order of .one part in ten million. In the drawing; Fig. 1 shows the essential Thus anything that tends tointroduce a spurlpartsof aspring gravimeter embodying the-inous angular deflection of, the spring detracts .vention; The spring comprises a helical portion,

source of error is the .eflect oi! improperly leveling the form shown; and an upper tapered portion theinstrument. It the ribbon springbe rigidly -l2 merging with the cylindrical portion. The attached to the support, the sensitivity. to levellower end of the spring isattached to a post l3 ing errors is sometimes 'as high as 1 milligal per as by rivets I4 and, an annular mass I5 is at- -10 10 seconds of arc oil level. (1 milligal is defined tached to the post. The mass hangs freely and 40 as an acceleratlonequal to 0.001 cm. per secis suspended by the spring. As shown, the tav v ond.) That is to say, if the instrument be 10 pered end of the spring is attachedas by rivets seconds oil? level, the spurious deflection intro- IS in a slot I] of a'threaded fixture I8 carried duced may be equivalent to a deflection produced in an adjusting plug l9 seatedin a conical seat by :1 1 milligal change in the acceleration of 20 of a fixed support 2|. Other means for at- 45 avity (0). ,With an accuracy requirement taching the spring to the fixture can be used, of 0.1'milligal a simple instrument must be leve.' g. soldering; the spring in all cases being rigideled to withinone second of are. This is diflicult ly attached to the supporting fixture, so as to of accomplishment in the field, especially if the form a unit therewith. v

150 ground is soft or swampy. In the application In operation, at a given-location on the earth there was disclosed away of reducing the level the spring and weight assume a definite position sensitivity, by providing; a filamentary suspension such as that shown in Fig. 1. Upon taking the or a flexible adjusting means for suspending the instrument to a region of difierent gravity, the spring. This lessens the, precision required in mass suifers a. change in weight, thereby changlevellng.'- I ing the stress on the spring. Thisresults in an 55 from the accuracy of the instrument. One I 10 formed by winding up a thin ribbon ll into 35 angular deflection of the spring, the maximum deflection being at the lower end thereof. This angular deflection is measured by suitable means (not shown) and is taken as a measure of the change of gravity.

Ordinarily, the tapering is applied to 5 to turns of the helix and the tapered portion extends approximately one-tenth the length of the spring.

Fig. 2 shows in exaggerated manner what takes place when the support is not accurately leveled.

The tapered portion of the spring is deflected but the main helical portion hangs vertical.

The success of the invention depends upon the facts that any bending of the ribbon spring is transformed into a rotation of the weight about the spring helix axis and that any spurious deand therefore tapering the top portion of the spring reduces the bending moment tending to distort the spring. These effects combine to reduce the sensitivity of the instrument to leveling errors. The mechanics of ribbon springs is complex, and it is probable that other more complicated factors also enter in; but in any case tapering the spring as described results, as a matter of fact, ,in a substantial decrease of level sensitivity.

It will be noted that the spring is rigidly attached to the support. This is of great advantage in that it provides the strongest possible attachment of the spring to the frame. The instrument withstands very rough handling; transportation in trucks, etc.

It has been found that the best results are se-' cured if the upper end of the spring leaves the supporting flxture of pin substantially horizontally, i; e. at right angles to the axis of the pin (or of the helix). Fig. 3 shows this arrangement, the ribbon being shown for the sake of clarity as pulled out flat. To secure the best results the ribbon should leavev the pin at an angle not departing more than about 5 degrees from a right angle.

In producing the spring, a pre-'formed helical ribbon is attached to the pin and the taper is introduced with the flngers, at first with no load on the spring and later with a part of the ultimate load. The tapered portiornis usually formed as a substantially conical helix. The flnishd spring is heat treated prior to use. The spring is usually embodied in metal or metal alloys.

While the invention has been described in reference to a gravimeter, it is applicable to other ilection is measured by suitable means (not shown). The top portion of the spring is tapered as in Fig. 1 and prevents spurious readings due to improperleveling. A barometer embodying a helical ribbon spring is disclosed in my copending application Serial No. 11,747, filed March 30, 1936.

If desired, a portion of the helix, e. g. one or two turns, can be made bimetallic, to compensate for temperature changes (which tend to cause a' spurious angular deflection of the spring). In Fig. 4 the lower portion of the helix is shown as comprising two ribbons of diflerent metals, indieating at 23 and 24, soldered or otherwise fastened to each other. Temperature compensation can be effected in other ways. For example, a separate short temperature compensating unit can be mounted-in series with the ribbon spring,

as disclosed in my acknowledged copending apthe helix so that such stress causes an angular;

deflection of the spring, the other end of the helix being tapered down to form a portion of diminished diameter. and means rigidly attached to the end of the ribbon at said tapered portionfor supporting the spring, the tapered portion preventing spurious rotations, due to improper alinement of the supporting-means with respect to the helix axis, from being communicated to the other end of the spring.

2. The apparatus of claim 1 wherein the axis of the ribbonat the end attached to the supporting means is substantially at right angles to the helix axis.

3. The apparatus of claim 1 wherein the tapered portion comprises from 5 tom turns of the helix and extends over approximately onetenth of the length of the helix.

4. In measuring apparatus, a vertically arranged helical coil spring formed of a wound-up thin ribbon, a massy body attached to the lower .end of the spring and supported thereby, the

upper end of the helix being tapered down to a portion of small diameter, and supporting means for the spring rigidly attached to the end of. the ribbon at the tapered portion, the tapered portion preventing inaccuracies in leveling of the supporting means from being communicated to the lower end of the spring;

5. In measuring apparatus, a helical coil spring formed of a wound-up thin ribbon, means for applying stress to the spring axially of the helix so that such stress causes an angular deflection of the spring, a majorportion of the spring consisting of a cylindrical helix and a minor portion of the spring consisting of a helix of smaller diameter having a substantially conical taper toward the end of the spring, and means rigidly attached to the, end of the tapered portion for supporting the spring, the tapered portion preventing spurious rotations due to improper alinement of the supporting means with respect to the helix axis, from being imparted to the end of the spring opposite the attached end.

ARCHERHOY'I. 

